1. to be the coolest of cool; this is the next level after 'cool as a cucumber'. People who are double cool with ice typically don't give a damn what anyone else thinks, can have fun anywhere/anytime, and give off such an insanely cool vibe that everyone else wants to be like them.

2. a way in which to order a drink if you want it in a very cold state.

dude: Wow, did you see that girl dance?
dude #2: Yeah man. She is definitely double cool with ice.

OR
girl: can you mix me a coke and rum, and make it double cool with ice?
bartender: for sure.